Upgrade django-postgres-extra to 1.21a11

Author: Photonios

setup.py

@@ -18,7 +18,7 @@
     author_email='[email protected]',
     keywords=['django', 'localized', 'language', 'models', 'fields'],
     install_requires=[
-        'django-postgres-extra>=1.21a',
+        'django-postgres-extra>=1.21a11',
         'Django>=1.11',
         'deprecation==2.0.3'
     ],